There is need to improve the accuracy of artillery shells fired by large bore weapons. Technological advances in metallurgy, propulsion, guidance and control now make it feasible for artillery systems to attack targets at ranges greater than 20 miles. Artillery shells follow a ballistic trajectory, which in an ideal world can be determined mathematically from launch point to target. However, the real world is not as forgiving. Numerous factors affect the trajectory. Variations in temperature, wind and precipitation along with minute differences in manufacturing tolerances of the projectile, the barrel of the weapon, and the charge are just a few of the factors affecting the flight of a projectile. Moreover, there is typically no control of the projectile after launch. Therefore, as the range increases, the potential impact footprint of the projectile grows until it reaches the point where the projectile can no longer be relied upon to accomplish the desired mission. There is a need then to improve the accuracy of artillery projectiles through in-flight guided control.
Modern artillery barrels are rifled so as to create spin in the projectile. Without spinning, the projectile has a tendency to tumble which makes it impossible to determine with any level of confidence where the projectile is going to land. One consequence of spin is that it creates a yawing to the right (with right hand refilling twist) or side slip angle called the yaw of repose. When a projectile is fired at a range of 20 miles, the yaw of repose will result in a cross range deflection of about 1 mile. In order to control a spinning projectile a design balance must be reached between the need for control surfaces and the need to maintain the spin.
There a number of relatively recent patents relating to gun launched guided projectiles, including: U.S. Pat. No. 6,126,109 which relates to an unlocking tail fin assembly; U.S. Pat. No. 7,163,176 drawn to a two-dimensional projectile guidance approach; U.S. Pat. No. 6,126,109 discloses a device for an unlocking tail fin assembly; U.S. Pat. No. 7,163,176 is a second patent drawn to a two-dimensional projectile guidance approach; U.S. Pat. No. 6,796,525 owned by the assignee of the present application, discloses a concept for roll isolation of the tail assembly from the body of the projectile; U.S. Pat. No. 6,866,775 discloses a stabilizing tail fin concept for a gun launched projectile; and U.S. Pat. No. 6,502,786 is a third patent disclosing a two-dimensional guidance approach. These designs, in general, include a section that allows for deployment and operation of a surface, such as a canard, that adjusts the flight path. However, none of the aforementioned patents discloses any means for effecting roll isolation for the guidance and control section of the projectile. Accordingly, there is a need in the industry for roll isolation of a fully guidance capable three-dimensional guidance and control section that is detachable from the projectile.